1 //===-- llvm/Use.h - Definition of the Use class ----------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This defines the Use class. The Use class represents the operand of an
11 // instruction or some other User instance which refers to a Value. The Use
12 // class keeps the "use list" of the referenced value up to date.
14 // Pointer tagging is used to efficiently find the User corresponding
15 // to a Use without having to store a User pointer in every Use. A
16 // User is preceded in memory by all the Uses corresponding to its
17 // operands, and the low bits of one of the fields (Prev) of the Use
18 // class are used to encode offsets to be able to find that User given
19 // a pointer to any Use. For details, see:
21 // http://www.llvm.org/docs/ProgrammersManual.html#UserLayout
23 //===----------------------------------------------------------------------===//
28 #include "llvm/ADT/PointerIntPair.h"
40 // Use** is only 4-byte aligned.
42 class PointerLikeTypeTraits<Use**> {
44 static inline void *getAsVoidPointer(Use** P) { return P; }
45 static inline Use **getFromVoidPointer(void *P) {
46 return static_cast<Use**>(P);
48 enum { NumLowBitsAvailable = 2 };
51 //===----------------------------------------------------------------------===//
53 //===----------------------------------------------------------------------===//
55 /// Use is here to make keeping the "use" list of a Value up-to-date really
59 /// swap - provide a fast substitute to std::swap<Use>
60 /// that also works with less standard-compliant compilers
63 // A type for the word following an array of hung-off Uses in memory, which is
64 // a pointer back to their User with the bottom bit set.
65 typedef PointerIntPair<User*, 1, unsigned> UserRef;
68 /// Copy ctor - do not implement
71 /// Destructor - Only for zap()
73 if (Val) removeFromList();
76 enum PrevPtrTag { zeroDigitTag
82 Use(PrevPtrTag tag) : Val(0) {
87 /// Normally Use will just implicitly convert to a Value* that it holds.
88 operator Value*() const { return Val; }
90 /// If implicit conversion to Value* doesn't work, the get() method returns
92 Value *get() const { return Val; }
94 /// getUser - This returns the User that contains this Use. For an
95 /// instruction operand, for example, this will return the instruction.
96 User *getUser() const;
98 inline void set(Value *Val);
100 Value *operator=(Value *RHS) {
104 const Use &operator=(const Use &RHS) {
109 Value *operator->() { return Val; }
110 const Value *operator->() const { return Val; }
112 Use *getNext() const { return Next; }
115 /// zap - This is used to destroy Use operands when the number of operands of
117 static void zap(Use *Start, const Use *Stop, bool del = false);
120 const Use* getImpliedUser() const;
121 static Use *initTags(Use *Start, Use *Stop);
125 PointerIntPair<Use**, 2, PrevPtrTag> Prev;
127 void setPrev(Use **NewPrev) {
128 Prev.setPointer(NewPrev);
130 void addToList(Use **List) {
132 if (Next) Next->setPrev(&Next);
136 void removeFromList() {
137 Use **StrippedPrev = Prev.getPointer();
138 *StrippedPrev = Next;
139 if (Next) Next->setPrev(StrippedPrev);
146 // simplify_type - Allow clients to treat uses just like values when using
147 // casting operators.
148 template<> struct simplify_type<Use> {
149 typedef Value* SimpleType;
150 static SimpleType getSimplifiedValue(const Use &Val) {
151 return static_cast<SimpleType>(Val.get());
154 template<> struct simplify_type<const Use> {
155 typedef Value* SimpleType;
156 static SimpleType getSimplifiedValue(const Use &Val) {
157 return static_cast<SimpleType>(Val.get());
163 template<typename UserTy> // UserTy == 'User' or 'const User'
164 class value_use_iterator : public std::iterator<std::forward_iterator_tag,
165 UserTy*, ptrdiff_t> {
166 typedef std::iterator<std::forward_iterator_tag, UserTy*, ptrdiff_t> super;
167 typedef value_use_iterator<UserTy> _Self;
170 explicit value_use_iterator(Use *u) : U(u) {}
173 typedef typename super::reference reference;
174 typedef typename super::pointer pointer;
176 value_use_iterator(const _Self &I) : U(I.U) {}
177 value_use_iterator() {}
179 bool operator==(const _Self &x) const {
182 bool operator!=(const _Self &x) const {
183 return !operator==(x);
186 /// atEnd - return true if this iterator is equal to use_end() on the value.
187 bool atEnd() const { return U == 0; }
189 // Iterator traversal: forward iteration only
190 _Self &operator++() { // Preincrement
191 assert(U && "Cannot increment end iterator!");
195 _Self operator++(int) { // Postincrement
196 _Self tmp = *this; ++*this; return tmp;
199 // Retrieve a pointer to the current User.
200 UserTy *operator*() const {
201 assert(U && "Cannot dereference end iterator!");
205 UserTy *operator->() const { return operator*(); }
207 Use &getUse() const { return *U; }
209 /// getOperandNo - Return the operand # of this use in its User. Defined in
212 unsigned getOperandNo() const;
215 } // End llvm namespace